A typical fuel cell is known to include an anode, a cathode, and a solid electrolyte layer disposed between the anode and the cathode (For example, reference is made to Japanese Patent Application Laid-Open No. 2009-228430).
In Japanese Patent Application Laid-Open No. 2009-228430, YSZ (yttria-stabilized zirconia) is used as the main component of the solid electrolyte layer.
It is known that there is a phase transformation of the zirconia contained in the solid electrolyte layer from cubic crystals to tetragonal crystals in the operating conditions of the fuel cell (reference is made for example to “Netsurikigakuteki Kaiseki in yoru Taikyusei Kojo no tame no Kiban Gijutsu Kaihatsu”, Haruo KISHIMOTO (nine others), Dec. 17 to 18, 2012, 21st SOFC Poster Session).
This zirconia phase transformation exhibits a tendency to progress from the anode side to the cathode side.